The present invention relates to magnetic field coils and more particularly to coils designed to produce a defined field in at least one volume.
In many applications it is important to provide a magnetic field the characteristic of which, for example, in an x-y plane is known. For example, in virtually every application of NMR spectroscopy and imaging it is essential to use magnetic fields whose spatial variation is controlled. Such fields may be uniform, or they may have a linear variation in either x, y or z (where x, y, z are the co-ordinate axes), or they may be uniform within a certain volume and rapidly changing elsewhere, as in TMR. For fine-tuning correction of nearly uniform main fields it is useful to have a set of shim coils, which provide known correction gradients, varying as xy, x.sup.2 -y.sup.2, yz etc.